Short wave capacitor



t Patented Dec. 12,v 1933 UNITED "STATES PATENT OFFICE 1,938,793' snoar WAVE cAPAcrToR William M. Bailey, Lynn, Mass., assgnor, `by mesne assignments, to General Electric Company, a corporation of New York Application VAugust 21, 1930. 'serial No. 476,820

4 claims. (ci. 17e-41) A This invention relates to short wave capacitors three terminals 21-23 are in circuit; but when of relatively high capacity and preferably also termina1s'21-22 only are in circuit, while the adapted for substantial current values. groups 11, 12, Fig. 1 being connected in parallel Where a number of armatures are connected With one another and the groups 13, 14 in parallel 5 in parallel, for short wave working, that is, withwith one another, yet groups 11, 12 being in series 60 out any short series connections, the direction of with groups 13, 14. When terminal 23 is in circurrent flow in each armature is the same`and cuit with only 21 or 22 then groups 11, 12 above there are no oppositely flowing currents in or groups 13, 14 above are in circuit and in different armatures to set up opposed magnetic parallel. An end plate 15 of aluminum, Fig: 1,

fields the result being that eddy current losses transmits the clamping created by the screws 65 in any metallic structure within the nonshown to maintain the stack of groups or sections neutralized magnetic eld becomesubstantial and in the stack under high mechanical compression contribute to the heating of the capacitor. between opposite metallic walls of casing 10.

To reduce such eddy current losses, the inten- Maple pressure blocks 16 and 17 separate each sities ofthe non-neutralized magnetic fields from end pair of groups or sections from one another, 70 one set of armatures acting on another set are while a much thicker pressure block 18 of the reduced in the present invention without reducsame material separates the successive pairs of ing the capacity value of the condensers due to groups or sections. Kiln dried maple is selected the parallel relations of the armatures this result for these blocks because of the low dielectric losses 20 being effected by providing the parallel conwithin maple and because such wood is slightly 75 nected armature foils with long leads into segrecompressible under the high mechanical comgated groups held under high mechanical compression which clamps the stack of segregated pression by spacing pressure blocks of insulating armature groups. material. This prevents the magnetic fields of The blocks 16 and 17 are of substantially the the several sections from being comparable in same thickness as the sections 13 `and 14 or the 30 intensity to what they would be inthe location sections 11 and 12. 'Ihe appropriate thickness of other sections if the groups were not separated for the blocks 16 and 17, as well as for the block by such insulating pressure blocks. Preferably 18 is all determined empirically by calculating the pressure blocks consist of an insulating matethe minimum separation for the sections which rial possessing low dielectric losses and. more results in the tolerable or minimum intensities of a5 compressible and cheaper than bakelite and the magnetic iields of one armature group at the like such as the wood of the maple tree. location of another group, and cause greatly the Because with very high frequencies the current eddy current losses and heating. With the Icirseems to be concentrated at the foil edges, it is cuit connections of Fig. 2, the insulating block desirable to have several spaced armature groups 18 is approximately three times as thick as any 90 or sections connected in parallel thus affording one block 16V or 17, i, e., it is of the same order a greater length for the edges along which the of thickness as the combined thickness of groups current concentrates and at the same time re- 13, 1,4 and block 16.` Since the direction'of the ducing the high frequency resistance of the foils, instantaneous current in each of the foils is in 40 whereby the current-carrying ability-of a conthe same direction, as above, the magnetic fields 95 denser of predetermined capacity is increased. due to each section are in the same direction Fig. 1 isalongitudinal section through one emand do not4 neutralize, but by separating the bodiment of this invention. armature groups by the insulating pressure blocks Fig. 2 shows the electrical connections for the as above the strength of the portions of the elds sections, while Fig. 3 shows the embedment enwhich overlap is reduced with consequent lower- 100 velope surrounding the separated groups or ing of eddy. current losses and heating; the insections. sulating blocks beingV outside the circuits and 'Ihe casing 10 enclosing ythe embedded groups preserving the parallel connections of the armais preferably an aluminum casting although other ture foils by the long leads extending thru the f material may be used if desired. The numerals spaces between the sides of the stack and the 105 .11, 12, 13 and 14 designate groups or sections of casing. The cover 19 is preferably of bakelite micas and metal foils, all arranged in a single and is secured in position by the screws illusstack the foils of each group or section, and the trated. On the cover are located the two termigroups or sections themselves, being all conl nals 21 and 22 while the opposite terminal 23 `is nected in parallel, as shown in Fig. 2 when all grounded to the metallic portions of the casing. 110

` The electrical connections will be more clearly lating material such as paraiiin the leads themselves;

of the armature-groups 1s obtained by the proviunderstood from` Fig. 2.

In Fig. 2 the central maple separator l is` While the armature-group 11 inFig. 1 shown contiguous to a side of the casingfit may, if desired, be spaced from the casing just as is the group 14 on the opposite side, in which event all the groups of armatures are enclosed in an envelope of embedment 20 as shown.v

The capacitor illustrated has been designed asa ilament by-pass condenser having relatively large capacity of the sections or groups of about .06 microfarad adapted for a wave length of 'only 15' `meters 4(25,000 kilocycles) at 200 volts 'and with a temperature rise of only about 15.

C. as the upper limit. The -high current-car- 'rying-J ability of the leads shown in Fig. 41 connecting the armature-groupsf 11, etc., with the terminals 21,- etc., provides for conduction of,

such heavy current without undue heating of but such high capacities sion of a number of armatures which as indicated in the drawing' constitutes a comparatively large mass of metal in each group, and such heavy current applied to the termin jlsof the capacitor,

sets up intense electromagnetic fields around each such group, so that, particularly at high frequency, such elds tend to cause high eddy current losses and harmful heating in any such mass of metal as these armature-groups which might lie in the denser portions of such intense electromagnetic ields around neighboring armaturegroups. vWhen the applied voltage'is comparatively low as above, even though the frequency -be high, electrostatic elds do not constitute any 4problem concerned with the masses of metal in :the armature-groups of high capacity. It is the electromagnetic fields which have caused the heating difficulties under these conditions. According to the present invention, not only are the leads between armature-groups and yterminals heavy enough to prevent undue heating by conduction of the high frequency currents of heavy amperage, but the tendency of such currents to cause eddy-current heating of the mass of metal in one armature group by the denser portions of intense electromagnetic elds around neighboring armature-groups, is' reduced to the desired amount by the low-cost, light Wooden spacers, so that even vunder such severe conditions of high frequency andlarge current, applied to the terminals of the high capacity condenser, the entire condenser including both special stack and high-current leads inside the casing, operates cool as desired, notwithstanding the comparatively large masses .of metal in the high capacity armature-groups, for the reason that by means of such spacers the mass of metal in each armature group is ,removed to a pointioutside the denser portions of the electromagnetic fields around neighboring armature-groups, so that no undesirable amount of heat is generated by eddy currents in any armature group. Since, therefore, all undesirable heating is thus prevented from' being generated in the rst place, there is obviated all need of removal of such heat if generated; i. e., it is not necessary to expose the stack .a l recense an embedment 20 of appropriate insu. i

armature group to air. or other cooling medium or otherwise, or to provide any heat-conductors, metal or otherwise in the stack adjacent the armature-groups, for the purpose of conducting heat therefrom and dissipating it to a cooler medium; but on the ther hand the invention permits the stack, ofv

esired high capacity and adapted to withstand application of the above high frequency currents y of high amperage, to be embedded in the cast--` ing 20 of wax or sulfur in casing 10 inthe ordinary way, just as if the devicewere of much lower capacity or as if the applied high frequency current were of low amperage; altho of course, as in any such case, the heavy leads to\ the terminals as shown do provide for ready conduction of some heat from the Iarmature groups to the terminals, the samebeing true in less degree of the wax or sulfur embedment 20, as to its conduction of a little heat from the armaturegroups to the metallic casing 10. But in accordance with thevinvention, substantially no heat is conducted from the' thermally and electrically insulating;v spacers of wood, which are eme bedded in and enclosed by the poorly heat-conducting embedment' 20 and thereby substantially heat-insulated from the metallic casing lsand the other two terminals 21, 22. On the other hand, the heavy leads connect the armaturegroups directly to the heat-dissipating casing 10 and terminals 21, 221 and serve to conduct to and dissipate in the .external atmosphere all heat generated in theleads themselves by the high -fre quency heavy current, it being unnecessary howeverI to provide for conduction and dissipation ofy heat generated by the intense fields generated by the high frequency heavy ap` plied current because all suchheat can be prevented .from being generated in the first place by the above arrangement of the wooden spacers designed With express relation to the high capacity and corresponding metallic massesof the armature-groups, and to :the high amperage of the applied high frequency current. Y The embodiment illustrated gives approximately from 25 to 50% better results from the stand- 120 point of heating or current carrying ability, than would be possible if the jinsulating separating pressureblocks were not used, and the armature groups were not separated or if the sections were separated but the pressure The desired. number of foils to each segregated is determined empirically and few are better than many., e'

Whatis claimed is: 1. A capacitor comprising a stack of sections 130 connected in parallel sc that theelds due to the currents in the armatures are in the same direction; separator blocks of insulating material in the stack between-successive sections, said sections being arranged in pairs with the blocks between `sections of eachpair thinner than the blocks between facing sections of the pairs; but the thinner blocks having substantial thickness substantially reducing heating inside the stack,.the respective blocks insulating and reducing heating inside the stack, the re; spective blocks insulating successive sections from one another in the stack.

2. A capacitor comprising a stack of sections connected in parallel so that the flelds due to the currents 'in the armatures are in the same direction, and a separator block of insulating material in the stack between sections, said'v sections being arranged in pairs with the blocks between the sections of each pair thinner than the blocks be- 150 electromagnetic -110 v blocks were of metal. l

along the stack thicknesses of tween the pairs, the thickness of the block between the pairs being at least about twice the thickness of the blocks between sections of a pair, all the blocks insulating successive sections from one another in the stack and having a thickness lsubstantially reducing heating inside the stack.

3. A capacitor comprising a stack of armature foils in combination with long leads extending from the sides of the stack and connecting the foils in parallel with one another, and means subjecting the ends of the stack to high mechanical compression; the foils being segregated into groups in the stack therein, each individual group including a comparatively small number of armatures; the armatures in' each individual group being separated by dielectric sheets insulating successive armatures from one another and having the same order of thickness as the armatures themselves; the individual groups of armatures being separated by dielectric blocks insulating successive groups from one another, having the same order of thickness as the groups themselves and lling the spaces between the groups; and the groups of groups of armatures being separated by a thick dielectric block insulating successive groups of groups from one another, and having the same order of thickness as the combined the groups of armatures and the dielectric blocks between said groups, said thick dielectric block lling the space between the adjacent groups of the groups of groups in the stack.

and into groups of groups capacitor of large capacity. which includes a casing including metallic and insulating portions and an enclosed stack held under high mechanical compression by and between opposite metallic walls of the casing, the sides of the stack being spaced from the casing walls; long leads extending from the armatures in the stackconnecting them in parallel and extending across the space between the stack and the casing; two terminals mounted on the insulating portion of the casing; said armatures and their intervening dielectric sheets being segregated in the stack into a plurality of groups each including a comparatively small number of armatures connected in parallel by said leads; and said groups themselves being segregated into groups also connected in parallel by said leads; insulating pressure blocks insulating successive armature groups from one another but filling the space between successive groups in each group of groups and having a thickness of thesame order of thickness as theindividual groups themselves; and an insulating block insulating the groups of groups from one another but illling the space between said substantially greater thickness than the aforesaid blocks; said long leads respectively extending from the armatures of the respective individual armature groups, and a set of said leads of one polarity being connected to a metallic portion of the casing.

WILLIAM M. BAILEY.

4. A short-wave groups of groups and having 

